Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

From: Li, ZhenHua
Date: Fri Apr 03 2015 - 05:02:45 EST

Hi Dave,

There may be some possibilities that the old iommu data is corrupted by
some other modules. Currently we do not have a better solution for the
dmar faults.

But I think when this happens, we need to fix the module that corrupted
the old iommu data. I once met a similar problem in normal kernel, the
queue used by the qi_* functions was written again by another module.
The fix was in that module, not in iommu module.


On 04/03/2015 04:40 PM, Dave Young wrote:
To fix this problem, we modifies the behaviors of the intel vt-d in the
crashdump kernel:

For DMA Remapping:
1. To accept the vt-d hardware in an active state,
2. Do not disable and re-enable the translation, keep it enabled.
3. Use the old root entry table, do not rewrite the RTA register.
4. Malloc and use new context entry table, copy data from the old ones that
used by the old kernel.

Have not read all the patches, but I have a question, not sure this has been
answered before. Old memory is not reliable, what if the old memory get corrupted
before panic? Is it safe to continue using it in 2nd kernel, I worry that it will
cause problems.

Hope I'm wrong though.


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